This invention relates to safety interlock switches which are designed to interrupt electrical circuit controlling internal moving components such that movement ceases when the interior of a machine is exposed. This type of system protects operators who can be injured by moving internal components while also preventing destruction of the internal components caused by contact with external elements while still in motion.
Safety interlock switches are ordinarily mounted adjacent removable lids, doors, or any type of cover and the like which, when opened, provide access into the interior of a machine, providing reach to internal components therein. When a cover is removed or opened, contact with the interlock switch is broken and the interlock switch is deactivated which breaks electrical circuit powering moving elements. When the cover is replaced and contact resumed, the electrical system is reactivated.
Conventional interlock switches are highly sensitive, having "travels" of about 1/25 to 1/16 of an inch. "Travel" is the margin of distance at which the switch will not deactivate when contact with a cover begins to break (also referred to as "play" when used in this context). This extremely limited travel available in conventional interlock switches causes problems with machines that have internal moving components which vibrate or rattle the entire apparatus. Vibrations and minute shiftings of a machine can inadvertently deactivate the interlock switch system due to its sensitivity. Any movement of a cover away from contact with an interlock switch that exceeds 1/16 of an inch travel can interrupt a machine's internal workings, bringing the activity to a halt. Operators faced with this dilemma have to constantly readjust covers to reactivate electrical circuit.
To illustrate this problem, one example is the use of safety interlock switches in storage apparatus in which internal moving components periodically shift stored items. As the stored contents are agitated, the cover is inadvertently pushed by the moving items. An interlock switch with limited travel distance mounted on such an apparatus will constantly deactivate the electrical system causing unnecessary cessation of the work activity of moving components and frustration to an operator faced with repeated stoppage.
One method that is currently being used to solve this problem is the use of leaf springs. Leaf springs are comprised of a flexible actuating arm connected to a pivot point. The flexible actuating arm is placed over a conventional interlock switch and interposed between the contact point of a cover and the switch. Since the cover and switch are separated by the actuating arm, the flexibility of the arm is intended to provide extra travel in an effort to extend the distance of actuation beyond the limited travel distances provided in the conventional interlock switch. The leaf springs are designed to push against the cover and the switch as the cover begins breaking contact in an attempt to delay deactivation.
Leaf springs can extend travel in interlock switches, but their endurance to repeated flexing over time is relatively low and have to be frequently replaced. Repeated bending of the actuating arms at pivot points causes loss of tension over relatively short periods of time. Furthermore, leaf springs have to be mounted off-center because the flexible actuating arm has to extend from its pivot point horizontally over an interlock switch causing complications in installment, especially since such installments have to be repeated frequently.
Another method of delaying actuation in interlock switches is the use of sophisticated magnetic sensing means. Magnetic sensors mounted to relevant machines are designed to detect breaks in contact between the cover and interlock switch and activate the switch through printed circuit logic if the travel exceeds a pre-programmed threshold distance. This threshold travel distance is programmed to be greater than the 1/16 of an inch available in conventional interlock switches. This type of system is relatively complicated and the costs of installing such a device is usually not justified. There is a need for an improved device which is of a simple construction for ease of incorporation into interlock switches and more economical in design to justify the amount of the return of adopting such an effort.
The present invention discloses a novel improvement over conventional interlock switch systems which can be cheaply incorporated with existing safety switches to create an economical and uncomplicated safety interlock switch mechanism.
It is an object of the present invention to provide an interlock switch system with increased travel distances to effectively extend actuation of conventional switches far beyond the distances currently possible.
It is an object of the present invention to provide an economical device which can easily be incorporated into machines with movable internal components to provide an optimal safety interlock switch mechanism which takes into consideration both safety and the practical demands of individual machines which may require more travel distances in its interlock switch.
It is a further object of the present invention to provide an improved safety interlock switch for decreasing the sensitivity required to deactivate the internal moving components in machines with excessive vibrations or machines which have internal workings which tend to inadvertently activate interlock switch mechanisms through their specific activity.
Other objects and improvements will be apparent to those skilled in the art in the following disclosure.